drop sd::LayoutMenu set_id overwrite

this was added with

commit d2b5ab3498a78c6d164a15b3bf2b947553ea2743
Date:   Sun Oct 20 09:50:48 2019 -0400

    sd: sidebar: force to set the id of the LayoutMenu control

    Otherwise, the function std::unique_ptr<UIObject>
    WindowUIObject::get_child(const OUString& rID)
    will not find the control with the rID.

    Change-Id: Ie571eb351bb0c59654f577cef1961247273d7608
    Reviewed-on: https://gerrit.libreoffice.org/81345

but there doesn't appear to be a current use of 'sd::LayoutMenu'
in LibreOffice or Online

Change-Id: I07ebd872f0dd203057c96386730acd5f6aa7a168
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/112141
Tested-by: Jenkins
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
diff --git a/sd/source/ui/sidebar/LayoutMenu.cxx b/sd/source/ui/sidebar/LayoutMenu.cxx
index 1f245ea..29b4350 100644
--- a/sd/source/ui/sidebar/LayoutMenu.cxx
+++ b/sd/source/ui/sidebar/LayoutMenu.cxx
@@ -165,7 +165,6 @@ LayoutMenu::LayoutMenu (
      mxSidebar(rxSidebar),
      mbIsDisposed(false)
{
    set_id("sd::LayoutMenu");
    implConstruct( *mrBase.GetDocument()->GetDocSh() );
    SAL_INFO("sd.ui", "created LayoutMenu at " << this);